1. Field of the Invention
The present invention relates to a method for measuring a quantity of usage of a device, in particular, to a method for measuring a quantity of usage of a CPU.
2. Background of the Related Art
There are various kinds of algorithms for predicting a quantity of usage of a system in the related art. In general, more complicated algorithms yield more credible predictions; less complicated algorithms yield less credible predictions.
In addition, a method for calculating a quantity of usage of a CPU can be differentiated in accordance with an operating system. For example, in a MS-Windows 9x system, system usage of a CPU is updated by the CPU itself using its own algorithm. However, it is recommended to use the registry information when an application program is developed.
Furthermore, because an Operating System (OS) kernel takes charge of the CPU multi-tasking in all threads in a present ready-to-run state, the OS kernel generally knows whether there are OS threads in the ready-to-run state or an action state (all threads do not wait for certain event to resume execution). For example, when the OS determines there are no threads in the ready-to-run state, a value of a power management timer is read, and the CPU is maintained in sleep mode. In this mode the power management timer operates independently from the CPU, and measures accurately time duration of reads (regular increase with a fixed rate of 3.579545 Mhz). After that, the OS reads the value of the power management timer when the CPU is waken up.
In addition, measuring time difference between initial timer read in the sleep mode of the CPU and second timer read in the wake mode is a measure of idle time of the CPU. In other words, the CPU idle time can be measured by dividing a total of the difference between the second timer and initial timer for a large sampling interval, by the sampling interval. It can be described as in Equations 1 and 2,Idle Ticks=Sum (across sampling interval)[Second Timer Read−Initial Timer Read]  [Equation 1]CPU Idle (%)=Idle Ticks×Tick Period(s)/Sampling Interval(s)×100%  [Equation 2]Herein, the first timer read describes a processor in sleep mode (initial timer read), and the second timer read describes the CPU is in the wake mode.
In contrast, related art algorithms yield large values of CPU usage, even though the system does not perform an operation. In addition, in the related art, there is no time interval information available for updating a quantity of usage of a CPU, accordingly it is not appropriate for measuring a quantity of usage of a CPU in short time. In addition, in the related art, because an algorithm has to be amended in order to adapt it to the MS-Windows system or a complicated code is required, it degrades the MS-Windows system performance.